Prosecutors have admitted that China is spying on Parliament despite suddenly dropping charges intended to bring suspected agents of Beijing to justice this week.
The Crown Prosecution Service (CPS) said it believes that the China Research Group of MPs had been targeted "as a means of obtaining information from within Parliament" on Government policy.
It is the first time that prosecutors have admitted that Parliament has been infiltrated by spies as part of an espionage operation run by Beijing.
The admission comes despite prosecutors earlier this week dropping a case against two alleged Chinese informants, who were accused of targeting the research group between 2021 and 2023.
Christopher Cash, 30, and Christopher Berry, 33, will no longer face prosecution for their alleged involvement in a Chinese plot, after prosecutors told the court that no evidence would be offered against them and the CPS "simply cannot continue to prosecute this case".
Both men denied any breach of the Official Secrets Act and said they were pleased the "nightmare" case was now over. They were formally found not guilty.
However, in a letter to Alicia Kearns, a Tory MP and member of the China Research Group, a CPS official admitted that her organisation had been targeted by China.
Frank Ferguson, head of the CPS's special crime and counter terrorism division, explained that the case had been dropped because "the evidential standard for the offence indicted is no longer met".
But he added: "I appreciate that you were operating in a context in which a research group chaired by you, which had access to other Parliamentarians as well as yourself, was unfortunately targeted by China as a means of obtaining information from within Parliament on the then government's policies and views in relation to China."
He said: "The CPS takes such conduct very seriously indeed as criminal offences which involve MPs threaten both the democratic process and public service."
The letter confirms for the first time that prosecutors believe China is targeting MPs to obtain information, beyond a series of cyber attacks reported by the Government in March 2024.
At the time, the UK government's National Cyber Security Centre (NCSC) said APT31, a China state-affiliated actor, was almost certainly responsible for targeting MPs' emails in 2021.
While the US government has repeatedly highlighted examples of Chinese state interference and espionage in political affairs, the UK has been less forthcoming.
The CPS has not explained why prosecutors had an apparent change of heart about their prosecution of Mr Cash and Mr Berry on Monday.
Ms Kearns told The Telegraph: "The CPS needs to come clean with Parliament and the public we serve: what witnesses or evidence was withdrawn, and by whom.
"The Government claims the CPS was wholly independent in this, yet the CPS, it appears, has either been gagged or is refusing to be honest with witnesses, let alone Parliament and the public, on why this case is not proceeding.
"It's beggar's belief for the CPS to concede we were being targeted by the Chinese state to obtain information on us and then, in the same letter, state they will not even attempt a prosecution.
"Where is the trial? Where is the due process? Will this be another scandal where it takes decades for the evidence to ever see the light of day?"
Mr Cash, a former parliamentary researcher linked to Ms Kearns and Tom Tugendhat, and Mr Berry, an academic, were arrested in March 2023 and accused of collecting information "for a purpose prejudicial to the safety or interests of the state" which could be "directly or indirectly, useful to an enemy".
They had been due to face trial at Woolwich Crown Court from October 6, but the CPS said on Monday that the evidence collected by the Met and parliamentary police had not met the threshold to continue prosecution.
That decision was criticised by the Home Office and Downing Street. A Home Office spokesman said it was "disappointing that they will not face trial given the seriousness of the allegations".
No10 added that the decision had been taken independently by the CPS, and that "any attempt by a foreign power to infiltrate our Parliament or democracy is unacceptable".
China dismissed the charges as a "self-staged political farce" and claimed they were "malicious slander".
Amid calls for an explanation for the decision, including from the Commons Speaker Sir Lindsay Hoyle, the CPS said no "outside pressure" was exerted on prosecutors to drop the charges.
Stephen Parkinson, the director of public prosecutions, said his team had considered "alternative offences" but concluded "none were suitable".
On Monday, Mr Cash's lawyer said he was "entirely innocent and should never have been arrested, let alone charged".
Speaking outside court, Mr Cash added: "While I am relieved that justice has been served today, the last two and a half years have been a nightmare for me and my family."